If the package length of a packaging web is not correct there may be trouble at the filling machine. Thus, it is important to check the packaging web concerning the package length and possibly the print repeat length. The package length (PL) is defined as the length of each package in the packaging web. The print repeat length (PRL) is defined as the length of each turn of the printing roller on the packaging web.
It is previously known to use photocells often combined with a pulse counter to measure package lengths or the like on packaging web. As photocells measure only in one point the position of the photocells has to be amended for measurement of different package webs. Furthermore, when using a pulse counter the package length is only measured indirectly and the measurement may be inaccurate due to slip between the web and the rollers or the like.